Add pg_get_role_ddl() function

Add pg_get_role_ddl() function

Add a new SQL-callable function that returns the DDL statements needed
to recreate a role. It takes a regrole argument and an optional VARIADIC
text argument for options that are specified as alternating name/value
pairs. The following options are supported: pretty (boolean) for
formatted output and memberships (boolean) to include GRANT statements
for role memberships and membership options. The return is one or
multiple rows where the first row is a CREATE ROLE statement and
subsequent rows are ALTER ROLE statements to set some role properties.
Password information is never included in the output.

The caller must have SELECT privilege on pg_authid.

Author: Mario Gonzalez <gonzalemario@gmail.com>
Author: Bryan Green <dbryan.green@gmail.com>
Co-authored-by: Andrew Dunstan <andrew@dunslane.net>
Co-authored-by: Euler Taveira <euler@eulerto.com>
Reviewed-by: Japin Li <japinli@hotmail.com>
Reviewed-by: Quan Zongliang <quanzongliang@yeah.net>
Reviewed-by: jian he <jian.universality@gmail.com>
Discussion: https://postgr.es/m/4c5f895e-3281-48f8-b943-9228b7da6471@gmail.com
Discussion: https://postgr.es/m/e247c261-e3fb-4810-81e0-a65893170e94@dunslane.net